Microphysical heating rates and PV modification in a warm conveyor belt: Comparison of a COSMO and IFS simulation

Transcription

1 Microphysical heating rates and PV modification in a warm conveyor belt: Comparison of a COSMO and IFS simulation Montreal, August 18th 2014 H. Joos1, M. Böttcher1, R. Forbes2 and H. Wernli1 1) IAC, ETH Zürich, Switzerland 2) ECMWF, Reading, UK

2 1) Introduction and Motivation WCB at 29 January Warm Conveyor Belts: - strongly ascending warm and moist airstreams in extratropical cyclones - formation of elongated cloud bands release of latent heat strong potential vorticity (PV) modification coupling of microphysics and dynamics Harrold,1973 Carlson, 1980 Browning, 1986 Wernli, 1997

3 1) Introduction and Motivation Main process behind PV modification: - strong formation of clouds in WCB diabatic heating modification of PV height PV maximum of diabatic heating + + PV

4 1) Introduction and Motivation Main process behind PV modification: - strong formation of clouds in WCB diabatic heating modification of PV height PV maximum of diabatic heating WCB trajectory PV along WCB + + PV ~ 800 hpa ~ 300 hpa pressure/

5 1) Introduction and Motivation Main process behind PV modification: - strong formation of clouds in WCB induces cyclonic circulation diabatic heating induces anti-cyclonic circulation modification of PV positive PV-anomaly in mid-troposphere height PV maximum of diabatic heating WCB trajectory negative PV-anomaly in upper troposphere PV along WCB + + PV ~ 800 hpa ~ 300 hpa pressure/

6 1) Introduction and Motivation Main process behind PV modification: - strong formation of clouds in WCB diabatic heating modification of PV 1) representation of clouds and microphysical heating rates along WCB trajectories in COSMO and IFS? 2) impact on PV modification? 3) implications for dynamics? height PV maximum of diabatic heating WCB trajectory PV along WCB + + PV ~ 800 hpa ~ 300 hpa pressure/

7 2) Method COSMO and IFS simulations of a WCB in January 2009 in the North Atlantic Setup: COSMO (regional) 28 km horizontal resolution, 60 vertical levels IFS (global) 25 km horizontal resolution, 60 vertical levels both models with operational NWP - setup - calculation of Diabatic Heating Rates and Diabatic PV Rates for every microphysical process. DHRtot = DHRcondensation + DHRdep. growth of snow + DHRmelting of snow DPVRmelting of snow +... DPVR ~ d/dz DHR DPVRtot = DPVRcondensation + DPVRdep. growth of snow

8 3) Case study: hydrometeors - 48 h forward trajectories ascent of 600 hpa in 48h ntra=14061 ntra=15114 mean hydrometeor mass along trajectories COSMO IFS

9 3) Case study: hydrometeors mean hydrometeor mass along trajectories IFS COSMO cloud water cloud ice snow rain total condensate

10 3) Case study: hydrometeors vertical cross section at 38 N hydrometeor mass COSMO snow IFS ice rain cloud water = trajectory intersection points

11 3) Case study: diabatic heating rates mean DHR along WCB trajectories COSMO IFS

12 3) Case study: diabatic heating rates mean DHR along WCB trajectories COSMO IFS total DHR condensation dep. growth convection melt. snow evap. rain

13 3) Case study: potential vorticity mean PV along WCB trajectories COSMO / IFS

14 2) Case study: diabatic PV rates mean DPVR along WCB trajectories COSMO IFS

15 2) Case study: diabatic PV rates mean DPVR along WCB trajectories COSMO IFS

16 3) Case study: PV and DPVRs low level PV and DPVR ( hpa) at 30 January 2009, 00 UTC COSMO IFS DPVR [pvu h-1] PV [pvu]

17 3) Case study: potential vorticity vertical cross section at 30 January 2009, 00 UTC at 38 N COSMO meridional wind position of WCB IFS

18 3) Case study: potential vorticity vertical cross section at 30 January 2009, 00 UTC at 38 N COSMO meridional wind V > 10 m/s position of WCB IFS V > 20 m/s

19 4) Outlook - sensitivity experiments with modified microphysical parameterization within one model isolates effect of microphysics on dynamics without influence from other parameterizations and grid resolutions - IFS and COSMO provide two different possible solutions need for detailed microphysical observations in order to constrain microphysical parameterizations and its effect on dynamics

20 5) Summary - calculation of DHR and DPVR in a WCB in COSMO and IFS 1) pronounced differences in representation of - cloud liquid, snow, ice, rain - diabatic heating rates 2) distinct differences in DPVR and PV evolution along WCB in lower and mid troposphere 3) differences in PV production in lower troposphere lead to pronounced differences in low-level wind field results emphasize importance of details in microphysics for dynamics of extratropical cyclones and the need for detailed measurements

21 3) Case study: diabatic heating rates Integrated DHRs along 48h WCB trajectories COSMO / IFS total DHR conden- convection dep. sation growth melt. snow evap. rain